Magnetic materials and their preparation



March 22, 1966 w. w. GILBERT ETAL 3,241,952

MAGNETIC MATERIALS AND THEIR PREPARATION Filed Feb. 28, 1963 W//PW/PE -g, INVENTORS BY GfK/ww@ ig/W ATTORNEY United States Patent Otice 3,241,952 MAGNETIC MATERIALS AND 'THEIR PREPARATION Walter W. Gilbert, Hockessin, Del., and Thomas .L Swoboda, Chester County, lia., assignors to E. l. du Pont de Nemours and Company, Wilmington, Del., a corporation of Delaware Filed Feb. 28, 1963, Ser. No. 261,784 13 Claims. (Cl. 75-134) This invention relates to magnetic materials and to methods Vfor their preparation. More particularly, it relates lto new magnetic compositions having a maximum saturation induction within a restricted temperature range and a much smaller induction at temperatures both above and below this range, and to methods for preparing such compositions.

Conventional magnetic materials are characterized by a saturation induction that decreases monotonically as temperature increases. Above a temperature termed the Curie temperature, or Curie point, the behavior of such material becomes that of a paramagnetic substance, but at lower temperatures, even as low as the boiling point of liquid helium and below, ferromagnetic behavior is retained and saturation inluction increases continuously as temperature decreases.

A few materials have been reported, such as suliides of chromium and iron, for which saturation induction increases with increasing temperature in a temperature range below the Curie point. The effect has not been well characterized in these materials, however, because of -an extremely critical dependence on metal-sulfur ratio and, especially for iron sulfide, on prior thermal history. Recently there have 'been developed several classes of magnetic compositions which exhibit a maximum saturation induction between K. and the Curie point of the composition. Such materials are described in copending applications Serial No. 66,194 of T. I. Swoboda, filed October 3l, 1960, now Patent No. 3,126,345, Serial No. 66,195 of T. A. Bither, filed October 31, 1960, now Patent No. 3,126,346 and Serial No. 181,744 of T. l. Swoboda, filed March 22, 1962, now Patent No. 3,126,- 347. Although these compositions possess desirable characteristics rendering them useful in a variety of devices for the interconversion of various forms of energy, and in other applications, it is worthwhile to provide new compositions based on readily available components which exhibit a maximum saturation induction within a useful temperature range.

The present invention provides a magnetic composition of the formula Mn2 X yTxT"ySbzIna, where T is chromium and/.or vanadium, T" is one or more of the rst row transition elements of Groups VIII and I-B, x is 0.003-0.25, y is 0.003-0.25, z is 0.50-10, and a is 0-0.50.

For better understanding of the present invention, reference is made to the following detailed description taken in connection with the accompanying drawing which is a typical magnetization-temperature plot for preferred compositions of this invention. The right-hand curve represents the plot obtained upon heating the composition While the left-hand curve represents the corresponding cooling plot. The temperature difference between these curves is the hysteresis value of the composition, usually measured at the transition midpoint.

As indicated in the above formula, manganese is an essential component of the compositions of this invention and is present to the extent of 5079.76 atom percent (based on the total of Mn, Sb, T and T). Likewise, antimony is an essential component and is present 3,241,952 Patented Mar. 22, 191,66

to the extent of 20.0-33.3 atom percent (also based on the total of Mn, Sb, T and T). The component T consists of at least one of chromium (at. No. 24) and vanadium (at. No. 23) and is present to an extent of 0.1-10.0 atom percent of the total of Mn, Sb, T and T. The component T" consists of at least lone metal of the group iron (at. No. 26), nickel (at. No. 28), cobalt (at. No. 27), and copper (at. No. 29). Thus, T can be (I) iron, nickel, cobalt, or copper each taken singly, (II) any two of these metals taken together, (III) any three of them taken together, or (IV) all four of these metals taken together. Compositions containing copper have been especially suitable for magnetic devices and it is preferred that component T be this metal. This component is present to the extent of 0.1-10.0 atoms percent (based on the total of Mn, Sb, T', and T"). Optionally, indium may be present in amounts up to 20 atom per,- cent of the total of Mn, Sb, T', and T".

The Periodic Table referred to herein is the table appearing in Demings General Chemistry, John Wiley & Sons, Inc., 5th ed., chapter l1.

It will be apparent from the foregoing that the cornpositions of this invention can be considered to be derived from a compound of manganese and antimony, MngSb, by replacement of part of the manganese by certain transition elements heretofore described, and, optionally, introduction of the element indium in addition to or as par.- tial replacement for antimony. Some deviation from the exact stoichiometry of the prototype may accompany such modifications in the MnZSb.

Specific compositions, according to the present invention include manganese-copper-chromium-indium antimonide, manganese-copper-vanadium antimonide, manganese-cobalt-chromium antimonide, manganese-ironchromium-indium antimonide, manganese-copper-chrommm-vanadium antimonide, manganese-nickelvanadium antimonide, manganese-cobalt-vanadium antimonide, and manganese-iron-copper-vanadium antimonide.

The novel compositions of this invention exhibit a tetragonal crystal structure, have a maximum saturation induction at atemperature in the range of to +150 C., and a Curie temperature above 150 C. Such compositions are useful in devices operating at temperatures near room temperatures. The unusual dependence of magnetization on temperature is believed to result from a transition from an antiferromagnetic state to a ferrimagnetic state with rise in temperature.

Compositions having a maximum saturation induction at ve-ry low temperatures can also be prepared and are especially useful in devices such as refrigerators and temperature-sensitive controls operating at temperatures near the boiling point of liquid nitrogen and below. The manner in which the exchange inversion varies with ternperature can be controlled by modifying -the composition lof the product. The best compositions exhibi-t avery low residual magnetism lbelow the lower magnetic transition temperature. In addition, many of these novel compositions exhibit little thermal hysteresis at low temperatures, a prerequisite to use in refrigeration devices.

These novel magnetic compositions are prepared by heating mixtures of the elements to a temperature in the range of 600 to 1400 C. In practice, temperatures of 700 to 1200 C. 4are usually employed. Temperatures of at least 850 C. are generally necessary if the composition is to be melted.

The time of heating is not critical but should be suilicient to permit complete reaction of the ingredients. In the examples below, heating times ranging up to about 16 hours were employed. However, longer times may be useful in some cases such as in the preparation of the compositions in single crystal form.

Heating may be carried -out at atmospheric pressure with the reactants protected by a blanket of inert gas such as helium or argon. Alternatively, the reaction may be conducted in an evacuated vessel. It is also possible to employ superatmospheric pressures. Small batches of product may be readily prepared by placing the ingredients in a quartz tube which is then evacuated and sealed. In this case, the reaction is carried out under the autogenous pressure developed by the reaction mixture at the reaction temperature.

The materials employed in preparing magnetic compositions of this invention can be the elements themselves or any of the binary or ternary combinations thereof, such as manganese antimonide, manganese-chromium antimonide, copper antimonide, and indium-manganese alloy. It is preferred that the materials be in powder or granular form and that they be well mixed before heating is commenced.

The starting materials are employed in such lrelative amounts that the resulting mixture contains the desired proportions of manganese, antimony, indium and the components T and T as defined above. These proportions are preferably ch-osen t-o fall within the ranges stated above since products prepared from such mixtures require a minimum of purification. It is possible, however, to prepare products of this invention from certain mixtures falling -outside the composition ranges stated. Of course such products will be contaminated with by-products and it is desirable to avoid extensive departure from the stated ranges.

After the desired heating cycle has been completed, the reaction mixture is slowly cooled lto room temperature and, if desired, subjected t-o purification, e.g., by extraction with acids or, after grinding, by magnetic separation. Alternatively, the product is quenched to a temperature below its melting point, and may then be annealed at a temperature above the quenching temperature but below (preferably close to) the melting point, followed by slow cooling to room temperature.

The novel compositions of this invention exhibit several magnetic characteristics which make them especially valuable for use in various specific applications. The novel lower magnetic transition temperature is a distin- -guishing feature conferring unusual utility on these materials. This temperature is determined in the same manner used for determination of ordinary Curie temperature, i.e., by the measurement of magnetic response as a function of temperature. It will, of course, be necessary in some instances to modify the usual equipment to the extent of providing means fo-r cooling the sample in addition to the usual heating means. A rapid method for determining qualitatively whether a product, which is magnetic at room temperature, possesses a low temperature magnetic transition point is to observe its magnetic behavior upon cooling to a low temperature such .as that of liquid nitrogen.

The new compositions of this invention and methods for their preparation are further illustrated by the following examples.

EXAMPLE I A powder blend, consisting of 1.08 g. of manganese, 0.195 g. of cobalt, 0.17 g. of'chromium, and 0.755 g. of antimony, was placed with 0.755 g. of indium chips in a quartz tube which was then evacuated and sealed. This blend contained Mn, Co, Cr, Sb, and In in the atom ratio of 6:1:1:2:2. The tube and contents were heated to 900 C. in a tube furnace, held at this temperature for 6 hours, and then furnace-cooled to room temperature. The porous, pale grey, highly crystallin-e product recovered from the tube was non-magnetic at the temperature of liquid N2, weakly magnetic at room temperature, and

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moderately magnetic at 100 C. A portion of the product was pulver-ized and the -saturation induction of the powder determined as a function of temperature. The novel lower magnetic transition occurred just above room temperature, and maximum saturation induction at ca. 56 C. The Curie point was approximately 164 C.

EXAMPLE II A powder blend of 2.30 g. of manganese, 0.04 g. of cobalt, 0.115 g. of chromium, and 2.72 g. of antimony (i.e., Mn187CO0,03Cr0,10SbL0) was added to an alumina crucible which had been baked at 950 C. and 10*5 mm. pressure overnight prior to loading. The crucible and contents were placed in a quartz tube within a vertical tube furnace and heated at 360 C. and 10-5 mm. pressure overnight. Evacuation was continued Iand the temperature was raised to 870 C. for 20 minutes and furthe-r to 950 C. for about 4 hours. The tube and contents were then cooled at 0.40 C./min. to 890 C. and waterquenched. After removal from the container, the boule thus produced was broken into 1-2 g. fragments composed of several large cystals each. These were sealed in a quartz tube and heated at 750 C. for 93 hours, then water-quenched. Ca. 0.2 g. of the product so obtained was crushed, and sealed in a small evacuated quartz tube equipped with thermocouple wells for measurement of magnetic response at various temperatures. The measurements were carried out in a non-uniform field of ca. 1000- 2000 gauss, and the measured force (proportion to magnetization) was plotted versus temperature. The transition temperature was found to be 68 C., the width of of the transition was 17 C., the residual magnetization was 2.2% of maximum magnetization, and the Curie temperature was 210 C.

EXAMPLE III The procedure of Example I was repeated using 2.033 g. of maganese, 0.104 g. of chromium, 0.056 g. of iron, and 2.435 g. of antimony (i.e., MnLB5CrOJOFeM5Sb). The product was a silvery, crystalline, porous slug. The transition temperature of this composition was 10 C.; the width of 80% of the transition was 46 C.; and the Curie temperature was 191 C.

EXAMPLES IV-XIX The elements enumerated in Table I were mixed in the ratios indicated in alumina crucibles which were placed in quartz envelopes. The mixtures were then heated to 400 C. under a vacuum of 10-4 mm. for a period of at least 2 hours, after which puriiied argon was admitted to a pressure just above atmospheric pressure. The mixtures were then heated well above the melting point (1100-1200 C.), maintained at this temperature for a period of 3 hours, and quenched under purified argon into a copper mold (.5 inner diameter by 2.5 outer diameter by 2.5 deep) cooled in ice water.

Annealing of the products was carried out in the following manner. The products were iirst heated in alumina crucibles in quartz envelopes to 400 C. under a vacuum of 10-4 mm. for a period of approximately 0.5 hour. Purified argon was then admitted and heating continued to an annealing temperature of 850 C., which was maintained for a period of one hour (unless otherwise specified in Table I). The product was then slowly cooled at 30 C./hr. under purified argon to room temperature. In Table I, Ts is the midpoint temperature of the transition curve as shown in the drawing; A80% is the transition temperature range over the middle 80% of the transition plot as in the drawing; hysteresis is the temperature difference between the midpoints of the heating and cooling curves; Rm is equal to the residual magnetization (B) divided by the maximum saturation induction (A), expressed as percent (see drawing); and Tc is the Curie temperature.

Table I Composition Magnetic properties Example No. Heating Hystere- Mn Cr Cu Sb In sis, C. Rm, To, O.

rTs, A080070, Y percent 1.95 0.02 0.03 0. ,95 0.05 -129 6 f 7 5 1. 75 0.10 0. 15 0.95 0. 05 80.2 5. 4 1. 4 0 1. 70 0. 15 0. 15 0. 95 0.05 127 7 2 5 1. 85 0. 02 0. 13 0. 95 0. 05 -93 7 6 9 1. 77 0. 10 0. 13 0. 95 0. 05 74 8 V7 4 1. 73 0. 15 v0. 13 0.95 0. 05 112 6 2 6 1. 76 0.09 0. 15 0.95 0.05 57 5 4 0 1.78 0. 15 0.07 0.95 0.05 87 7 3 2 1.88 0.05 0.07 -0. 95 0.05 .-30 7 2 8 l. 76 v0. 09 0. 15 0. `95 0.05 71. 2 v0. 0 l. 8 0 1. 74 r0.11 0.15 0.95 0.05 94. 2 6. 2 1.8 0

Mn `V Cu Sb' In 1.75 `0. 10 .0. 15 0.95 0.05 13. 5 15 2 5 183 0. 02 0. 15 `0. 95 0. 05 -84 1l 4 5 1.87 0. l 0.03 0.95 A' 0.05 -17 11 2 9 I n Cr" C0 Sb 'In i Mn Cr Ni vSb i In Mn 'Cr ori sb In XXI 4 1. 886 0. 101 0.003 0.980 0.020 +31 3. 8 2. 1 0

Mn Cr Cu Sb 'In XXII 4 1. 872' ,0. 00,15 '0.125 n'0. 95o 16.050 145 10 23 17 Mn V Co Y Sb l A I n XXIII 4 1. 971 `0. 026 .0. 003 o. 950 0. 050 14s 2 13 o Mn Cr Cu Sb In Y XXIV 1. 65 o. 1o o. 25 0195 t 0.05 +111 1,5 5 0 185 1 Annealed 0.5 hour. 2 Annealed at 780 C. 3 Annealed at 800 C. .4 Quenehed for 3.5 hours.

VThe novel products of this invention are useful in devices for the interconversion and control of various forms of energy such as solar motors, temperature-sensitive inductors, thermally activated clutches, and in temperature compensators in devices based on conventional magnetic materials, Where sagging of magnetic properties with `increased temperature is functionally deleterious. In-their essential features, all of these devices comprise at least three components, namely, the magnetic component described above, means forapplying a form of energy to and from the magnetic component, and means for utilizing the output from the magnetic component. For some applications, the devices may include means for controllably magnetizing and demagnetizing the magnetic component. At temperatures Within `the ferromagnetic range, these compositions can be used in any of the conventional applications for ferromagnetic materials for which their properties render them suitable, e.g., electromagnets, high frequency coil cores, information and memory storage elements, and the like. The small thermal hysteresis of some of the compositions of this invention make them especially suitable for use in refrigeration devices.

As many widely different embodiments of this invention may be made without departing from the spirit and scope thereof, it is to be understood that this invention products were heated 115,400 C., for tlnours at 1 0-4 mm. pressure, and annealing temperature (850 C.) maintained is not limited to the specific embodiments thereof except as defined in the appended claims.

`The embodiments of ythe invention in which an eX- clusive property or privilege is claimed are defined as follows:

1. Magnetic compositions of the formula wherein Tf consists of at least one element of atomic number 23-24 inclusive, T consists of at least one element of atomic number 26-.29 inclusive, x is a nu merical value in the range 0.003 Vto 0.25 inclusive, y is a numerical value in the range 0.003 to 0.25 inclusive, a is a numerical value in the range 0.50 to 1.0 inclusive and Ffa is a numerical value yin the range 0 to 0.50 inclusive, said compositions exhibiting tetragonal crystal structure.

`2. Magnetic Vcompositions `of the formula wherein T consists of at least one element of atomic number 23-24 inclusive, T consists of an element of atomic number 26-29 inclusive, x is a numerical value in the ran-ge 0.003 to 0.25 inclusive, y is a numerical value in the range 0.003 to 0.25 inclusive, z is a numerical value in the range 0.50 to 1.0 inclusive and a is a numerical value in the range to 0.50 inclusive, said compositions exhibiting tetragonal crystal structure.

3. Magnetic compositions of the formula wherein T consists of an element of atomic number 23-24 inclusive, T consists of an element of atomic num-ber 26-29 inclusive, x is a numerical value in the range 0.003 to 0.24 inclusive, y is a numerical value in the range 0.003 to 0.25 inclusive, z is a numerical value in the range 0.80 to 1.0 inclusive and a is a numerical value in the range 0 to 0.20 inclusive, said compositions exhibiting tetragonal crystal structure.

4. The magnetic compositions defined in claim y3 wherein T represents chromium and T represents copper.

5. The compositions defined in claim 3 wherein T' represents vanadium and T" represents copper.

6. The magnetic composition of the formula Mnl .sicoaoacfonosbro said composition exhibiting a tetragonal crystal structure.

7. The magnetic composition of the formula said composition exhibiting a tetragonal crystal structure.

8. The magnetic composition of the formula Mflrsscfo.ozcuuoasbossndos said composition exhibiting a tetragonal crystal structure.

9. The magnetic composition of the formula Mnmscfo.locuonssbosslnaos said composition exhibiting a tetragonal crystal structure.

10. Process for the formation of a magnetic composition exhibiting a tetragonal crystal structure of the formula Mn2 x yT'xTySbzIna wherein T consists of at least one element of atomic number 23-24 inclusive, T" consists of at least one element of atomic number 26-29 inclusive, x is a numerical value in the range 0.003 to 0.25 inclusive, y is a numerical value in the range 0.003 to 0.25 inclusive, "z is a numerical value lin the range 0.50 to 1.0 inclusive and a is a numerical value in the range 0 to 0.50 inclusive which comprises mixing the desired proportions of Mn, T', T", Sb and In, heating the resultant mixture in an inert environment at a temperature in the range 600 C. to l400 C. for a period of time sufficient to permit essentially complete reaction of the ingredients and slowly cooling the resultant product to room temperature.

11. Process for the formation of a magnetic composition exhibiting a tetragonal crystal structure of the formula wherein T consists of an element of atomic number 23-24 inclusive, T consists of an element of atomic number 26-29 inclusive, x is a numerical value in the range 0.003 to 0.25 inclusive, y is a numerical value in the range 0.003 to 0.25 inclusive, z is a numerical value in the range 0.50 to 1.0 inclusive and a is a numerical value in the range 0 to 0.50 inclusive which comprises mixing the desired proportions of Mn, T', T", Sb and In, heating the resultant mixture in an inert environment at a temperature in the range 700 C. to

8 1200 C. for a period of time sufiicient to permit essentially complete reaction of the ingredients and slowly cooling the resultant product to room temperature.

12. Process for the lformation of a magnetic composition exhibiting a tetragonal crystal structure of the formula wherein T' consists of at least one element of atomic number 23424 inclusive, T" consists of at least one element of atomic num-ber 26-29 inclusive, x is a numerical value in the range 0.003 to 0.25 inclusive, y is a numerical value in the range 0.003 to 0.25 inclusive, z is a numerical value in the range 0.50 to 1.0 inclusive and a is a numerical value in the range 0 to 0.50 inclusive which comprises mixing the desired proportions of Mn, T', T, Sb, and In, heating the resultant mixture in an inert environment at a temperature in the range 700 C. to 1400 C. for a period of time sufficient to permit essentially complete reaction of the ingredients, cool-ing the resultant product by quenching to a temperature below its melting point, annealing said product at a temperature above the quenching temperature but below its melting point and slowly cooling said product to room temperature.

13. Process for the formation of a magnetic composition exhibiting a tetragonal crystal structure of the formula wherein T consists of at least one element of atomic number 23-24 inclusive, T" consists of at least one element of atomic number 26-29 inclusive, x is a numerical Value in the range 0.003 to 0.25 inclusive, y is a numerical value in the range 0.003 to 0.25 inclusive, z is a numerical value in the range 0.50 to 1.0 inclusive and a is a numerical value in the range 0 to 0.50 inclusive which comprises mixing the desired proportions of Mn, T', T, Sb and In, heating the resultant mixture at a pressure of about l04 mm. of Hg and at a temperature of about 400 C. for Ia period of approximately 2 hours, heating at atmospheric pressure and in an environment of a purified inert gas at a temperature in the range 1100 C. to l200 C. for a period of approximately 3 hours, cooling the resulting product by quenching to a temperature of approximately 0 C., annealing the resultant solid product by heating first at a pressure of about 10-4 mm. of Hg and at a temperature of about 400 C. for approximately 0.5 hour and then at atmospheric pressure, in an environment of a purified inert gas and at a temperature close to but below the melting point of said product for a period of about l hour and cooling said product to room temperature at a rate of approximately 30 C./hr. and in an environment of a puried inert gas.

References Cited bythe Examiner FOREIGN PATENTS 1/ 1910 Great Britain.

OTHER REFERENCES Bozorth: Ferromagnetism, D. Van Nostrand Co., Inc. (New York, 1951, pages 19-29, 328, 334 and 335).

TOBIAS E. LEVOW, Primary Examiner.

MAURICE A. BRINDISI, Examiner. 

1. MAGNETIC COMPOSITIONS OF THE FORMULA
 10. PROCESS FOR THE FORMATION OF A MAGNETIC COMPOSITION EXHIBITING A TETRAGONAL CRYSTAL STRUCTURE OF THE FORMULA 